1. Field of the Invention
This invention relates to a camera system having a focus detecting apparatus which mitigates the influence of vignetting.
2. Description of the Related Art
As the focus detecting apparatus of a TTL camera, there are known so-called pupil division type automatic focus detecting apparatus for detecting the focus-adjusted state of a photo-taking optical system from the relative amount of displacement of a plurality of object images produced by light beams coming from different areas of the pupil of the photo-taking optical system.
For example, U.S. Pat. No. 4,185,191 discloses an automatic focus detecting apparatus of this type constituted by a pair of arrays, i.e., a lens array disposed near a primary image surface and a light-receiving element array disposed immediately rearwardly thereof.
Also, U.S. Pat. No. 4,264,810 discloses an automatic focus detecting apparatus of this type constituted by a field lens disposed on a primary image surface, two re-imaging lenses for re-imaging on a secondary image surface the image formed on the primary image surface, and two image sensor arrays disposed on the secondary image surface.
However, such pupil division type automatic focus detecting apparatus according to the prior art have suffered from the following disadvantage.
In the automatic focus detecting apparatus of this type, the pupil of a predetermined F-number is specified on a plane orthogonal to a predetermined position on the optic axis by the optical system on the focus detection side and therefore, even if the F-number of the exit pupil is greater than said predetermined F-number or the F-number of the exit pupil is equal to or smaller than said predetermined F-number, when an interchangeable lens having an exit pupil position different from said predetermined position is mounted on a camera body having said automatic focus detecting apparatus, vignetting is sometimes produced in the focus detecting light beam by the exit pupil, and when the vignetting becomes non-uniform on the image surface of the focus detecting optical system side, the image of the object to be photographed is distorted and thus, it has been impossible to accomplish accurate focus detection.